Spliceosome is best described as what?

• A. A protein complex that translates codons.
• B. A DNA sequence that initiates transcription.
• C. A ribosome.
• D. A ribonucleoprotein complex that catalyzes intron removal.

Answer: (D)

Spliceosome is the cellular machine in the nucleus that removes introns from pre-mRNA. It’s a ribonucleoprotein complex, meaning it’s built from RNA components (snRNA) and proteins that come together to form the catalytic core. The RNA parts help recognize splice sites and drive the two chemical steps that cut out introns and join the exons, a process called splicing. This RNA-driven catalysis, supported by proteins, is what makes it the correct description: a ribonucleoprotein complex that catalyzes intron removal. It's not responsible for translating codons (that’s the ribosome), nor is it a DNA sequence that starts transcription (a promoter), nor is it the ribosome itself.